Experiment: Permeability Test by Variable Head Permeameter
Object:
To determine the co-efficient of permeability of soil by variable head
permeameter.
Apparatus
:
1. Stopwatch, 2. Scale, 3. Permeameter
Theory: The variable head permeameter consists of
a brass-mould in which soil samples can be compacted or undisturbed samples can
be placed. Fine copper wire mesh and perforated plates are fitted at the
top and the bottom of the mould and it
is kept in a constant level rough. The top is connected to a glass-stand-pipe
of suitable size. At any instant, the head of water equals the scale reading
(N) , plus the difference (M) in elevation of the zero of the scale and the
water level is the through. It can be proved on the basis of Darcy’s law for
flow through soils that the coefficient of permeability.
K= 2.3(aL /At ) (log10 h0-log10
h1)
Where, a = area of cross section of the stand
pipe
L= length of the soil
sample
A= area of
cross-section of the soil sample
h0 = initial
head of water
h1 = the
head of water after a time ‘t’
Procedure:
1. Water is filled in the standpipe which is
being used. The stopcock at the top of the parameter is closed after the
expulsion of all the air from the rubber tube and the connecting pipe.
2. If the soil is not
already saturated, it is left for about 24 hours for saturation, the rough is
filled up to the top.
3.The stand pipe is
filled with water, almost upto the top, after tightening the clamp on the
rubber tube.
4. The clamp is
released, when the water level in the standpipe starts falling, steadily, it is
read and simultaneously the stop watch is started.
5. The flow of water is
stopped when the water level in the standpipe falls through a sufficient
distance as indicated in the table ( see text page) and the time noted.
6. Five sets of such
independent readings are taken and an average values of the co-efficient of
permeability ‘K’ is found out.
Observations
and Computations:
Diameter of
standpipe :
...........................................................
3.The stand pipe is
filled with water, almost upto the top, after tightening the clamp on the
rubber tube.
4. The clamp is
released, when the water level in the standpipe starts falling, steadily, it is
read and simultaneously the stop watch is started.
5. The flow of water is
stopped when the water level in the standpipe falls through a sufficient
distance as indicated in the table ( see text page) and the time noted.
6. Five sets of such
independent readings are taken and an average values of the co-efficient of
permeability ‘K’ is found out.
Observations
and Computations:
Diameter of
standpipe :
.................................................................................
Zero of scale and water
level in the rough (=M)
:..........................................
Cross sectional area of
sample :
...................................................................
Cross sectional area of
the standpipe : .........................................................
Height of the
sample :
...................................................................................
Obs.
No.
|
Scale
|
reading
|
Time
|
Total
|
Head
|
Value
|
|
N0
(at ti-
me’
|
N1
(at ti-
me’
|
elapsed,
|
at’
t=0
|
at’
t=1
|
of
‘K
|
Average
|
|
t=0
(cm
)
|
t=1
( cm
)
|
t
(sec)
|
h0=
N0+
M
(cm)
|
h1=
N1+
M
(cm)
|
(cm/sec)
|
(cm/sec)
|
|
1
|
80
|
25
|
|||||
2
|
75
|
20
|
|||||
3
|
70
|
15
|
|||||
4
|
65
|
10
|
|||||
5
|
60
|
05
|
Zero of scale and water level in the rough (=M)
AFTER PUTTING THE ALL ABOVE DATA YOU CAN FIND THE PERMEABILITY THROUGH SOIL:
Co-efficient of
permeability of the given soil sample was found to be .................................... cm/sec.
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